diff --git a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_alert_types/threshold/expression.tsx b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_alert_types/threshold/expression.tsx
index 5c7f48de81f75..728418bf3c336 100644
--- a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_alert_types/threshold/expression.tsx
+++ b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_alert_types/threshold/expression.tsx
@@ -50,7 +50,7 @@ const DEFAULT_VALUES = {
   THRESHOLD_COMPARATOR: COMPARATORS.GREATER_THAN,
   TIME_WINDOW_SIZE: 5,
   TIME_WINDOW_UNIT: 'm',
-  THRESHOLD: [1000, 5000],
+  THRESHOLD: [1000],
   GROUP_BY: 'all',
 };
 
diff --git a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_alert_types/threshold/index.ts b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_alert_types/threshold/index.ts
index a94d2319d6e4d..b8ad623e23424 100644
--- a/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_alert_types/threshold/index.ts
+++ b/x-pack/plugins/triggers_actions_ui/public/application/components/builtin_alert_types/threshold/index.ts
@@ -7,7 +7,11 @@ import { i18n } from '@kbn/i18n';
 import { AlertTypeModel, ValidationResult } from '../../../../types';
 import { IndexThresholdAlertTypeExpression } from './expression';
 import { IndexThresholdAlertParams } from './types';
-import { builtInGroupByTypes, builtInAggregationTypes } from '../../../../common/constants';
+import {
+  builtInGroupByTypes,
+  builtInAggregationTypes,
+  builtInComparators,
+} from '../../../../common/constants';
 
 export function getAlertType(): AlertTypeModel {
   return {
@@ -26,6 +30,7 @@ export function getAlertType(): AlertTypeModel {
         termField,
         threshold,
         timeWindowSize,
+        thresholdComparator,
       } = alertParams;
       const validationResult = { errors: {} };
       const errors = {
@@ -84,20 +89,32 @@ export function getAlertType(): AlertTypeModel {
           )
         );
       }
-      if (threshold && threshold.length > 0 && !threshold[0]) {
+      if (!threshold || threshold.length === 0 || (threshold.length === 1 && !threshold[0])) {
         errors.threshold0.push(
           i18n.translate('xpack.triggersActionsUI.sections.addAlert.error.requiredThreshold0Text', {
             defaultMessage: 'Threshold0, is required.',
           })
         );
       }
-      if (threshold && threshold.length > 1 && !threshold[1]) {
+      if (
+        thresholdComparator &&
+        builtInComparators[thresholdComparator].requiredValues > 1 &&
+        (!threshold ||
+          (threshold && threshold.length < builtInComparators[thresholdComparator!].requiredValues))
+      ) {
         errors.threshold1.push(
           i18n.translate('xpack.triggersActionsUI.sections.addAlert.error.requiredThreshold1Text', {
             defaultMessage: 'Threshold1 is required.',
           })
         );
       }
+      if (threshold && threshold.length === 2 && threshold[0] > threshold[1]) {
+        errors.threshold1.push(
+          i18n.translate('xpack.triggersActionsUI.sections.addAlert.error.requiredThreshold1Text', {
+            defaultMessage: 'Threshold1 should be > Threshold0.',
+          })
+        );
+      }
       return validationResult;
     },
     defaultActionMessage: 'Alert [{{ctx.metadata.name}}] has exceeded the threshold',
diff --git a/x-pack/plugins/triggers_actions_ui/public/common/expression_items/threshold.test.tsx b/x-pack/plugins/triggers_actions_ui/public/common/expression_items/threshold.test.tsx
index bd3c7383d4b9c..92880bd124507 100644
--- a/x-pack/plugins/triggers_actions_ui/public/common/expression_items/threshold.test.tsx
+++ b/x-pack/plugins/triggers_actions_ui/public/common/expression_items/threshold.test.tsx
@@ -15,7 +15,7 @@ describe('threshold expression', () => {
     const wrapper = shallow(
       <ThresholdExpression
         thresholdComparator={'between'}
-        errors={{ threshold0: [] }}
+        errors={{ threshold0: [], threshold1: [] }}
         onChangeSelectedThreshold={onChangeSelectedThreshold}
         onChangeSelectedThresholdComparator={onChangeSelectedThresholdComparator}
       />
@@ -59,7 +59,7 @@ describe('threshold expression', () => {
     const wrapper = shallow(
       <ThresholdExpression
         thresholdComparator={'between'}
-        errors={{ threshold0: [] }}
+        errors={{ threshold0: [], threshold1: [] }}
         onChangeSelectedThreshold={onChangeSelectedThreshold}
         onChangeSelectedThresholdComparator={onChangeSelectedThresholdComparator}
       />
diff --git a/x-pack/plugins/triggers_actions_ui/public/common/expression_items/threshold.tsx b/x-pack/plugins/triggers_actions_ui/public/common/expression_items/threshold.tsx
index ecbf0aee63e2d..2dda0a576cea5 100644
--- a/x-pack/plugins/triggers_actions_ui/public/common/expression_items/threshold.tsx
+++ b/x-pack/plugins/triggers_actions_ui/public/common/expression_items/threshold.tsx
@@ -105,6 +105,11 @@ export const ThresholdExpression = ({
               value={thresholdComparator}
               onChange={e => {
                 onChangeSelectedThresholdComparator(e.target.value);
+                const thresholdValues: number[] | undefined = [];
+                Array.from(Array(comparators[e.target.value].requiredValues)).map((_notUsed, i) => {
+                  thresholdValues.push(threshold[i] ?? 0);
+                });
+                onChangeSelectedThreshold(thresholdValues);
               }}
               options={Object.values(comparators).map(({ text, value }) => {
                 return { text, value };
@@ -123,12 +128,14 @@ export const ThresholdExpression = ({
                   </EuiFlexItem>
                 ) : null}
                 <EuiFlexItem grow={false}>
-                  <EuiFormRow>
+                  <EuiFormRow
+                    isInvalid={errors[`threshold${i}`].length > 0 || !threshold[i]}
+                    error={errors[`threshold${i}`]}
+                  >
                     <EuiFieldNumber
                       data-test-subj="alertThresholdInput"
-                      value={!threshold || threshold[i] === null ? 0 : threshold[i]}
-                      min={0}
-                      step={0.1}
+                      value={!threshold || !threshold[i] ? 0 : threshold[i]}
+                      isInvalid={errors[`threshold${i}`].length > 0 || !threshold[i]}
                       onChange={e => {
                         const { value } = e.target;
                         const thresholdVal = value !== '' ? parseFloat(value) : undefined;